Method and apparatus for resonant gas phase acousto-optic modulation

Abstract

A method and apparatus for resonant gas phase optical phase modulation is disclosed. The method may include passing a laser beam longitudinally through a tube open to air at both ends and setting air inside the tube into resonant acoustic oscillation, thereby temporally modulating the refractive index of the air, which temporally modulates the optical phase of the laser beam.

I claim: 
     
       1. A method for resonant gas phase optical phase modulation, comprising:
 passing a laser beam longitudinally through a tube open to air at both ends; and 
 setting air inside the tube into resonant acoustic oscillation, thereby temporally modulating the refractive index of the air, which temporally modulates the optical phase of the laser beam, 
 wherein the acoustic transducer used to excite the resonant acoustic oscillation within the tube creates acoustic oscillation such that one acoustic wavelength is slightly longer than twice the tube length. 
 
     
     
       2. The method of  claim 1 , further comprising using an acoustic transducer to set the air inside the tube into resonant acoustic oscillation. 
     
     
       3. The method of  claim 2 , wherein the acoustic transducer is near a center of the tube. 
     
     
       4. The method of  claim 1 , wherein acoustic pressure oscillates at high amplitude near the center of the tube and tapers to near zero at both ends of the tube. 
     
     
       5. The method of  claim 1 , wherein a refractive index of the air inside the tub varies periodically with air pressure, thereby imposing a sinusoidal phase modulation with a period of acoustic resonance on the laser beam passed lengthwise through the tube. 
     
     
       6. The method of  claim 5 , further comprising incorporating the gas phase optical phase modulation into an optical homodyne self-diffraction densitometer. 
     
     
       7. An apparatus for resonant gas phase optical phase modulation, comprising:
 a tube open to air at both ends through which a laser beam is passed longitudinally; and 
 an acoustic transducer within the tube to set air inside the tube into resonant acoustic oscillation, thereby temporally modulating the refractive index of the air and temporally modulating the optical phase of the laser beam, 
 wherein the acoustic transducer used to excite the resonant acoustic oscillation within the tube creates acoustic oscillation such that one acoustic wavelength is slightly longer than twice the tube length. 
 
     
     
       8. The apparatus of  claim 7 , wherein the acoustic transducer is near a center of the tube. 
     
     
       9. The apparatus of  claim 7 , wherein acoustic pressure oscillates at high amplitude near the center of the tube and tapers to near zero at both ends of the tube. 
     
     
       10. The apparatus of  claim 7 , wherein a refractive index of the air inside the tub varies periodically with air pressure, thereby imposing a sinusoidal phase modulation with a period of acoustic resonance on the laser beam passed lengthwise through the tube. 
     
     
       11. The apparatus of  claim 10 , wherein said apparatus is operable in an optical homodyne self-diffraction densitometer. 
     
     
       12. A resonant gas phase acousto-optic modulator, comprising:
 an open ended cylinder without optical surfaces through which a laser beam is passed longitudinally; and 
 an acoustic transducer within the cylinder to set air inside the cylinder into resonant acoustic oscillation, thereby temporally modulating the refractive index of the air and thus temporally modulating an optical phase of the laser beam, 
 wherein the acoustic transducer used to excite the resonant acoustic oscillation within the cylinder creates acoustic oscillation such that one acoustic wavelength is slightly longer than twice the cylinder length. 
 
     
     
       13. The resonant gas phase acousto-optic modulator of  claim 12 , wherein the acoustic transducer is near a center of the cylinder. 
     
     
       14. The resonant gas phase acousto-optic modulator of  claim 12 , wherein acoustic pressure oscillates at high amplitude near the center of the cylinder and tapers to near zero at both ends of the cylinder. 
     
     
       15. The resonant gas phase acousto-optic modulator of  claim 12 , wherein a refractive index of the air inside the cylinder varies periodically with air pressure, thereby imposing a sinusoidal phase modulation with a period of acoustic resonance on the laser beam passed lengthwise through the cylinder. 
     
     
       16. The resonant gas phase acousto-optic modulator of  claim 15 , wherein said apparatus is operable in an optical homodyne self-diffraction densitometer. 
     
     
       17. A non-transient computer-readable medium storing instructions for resonant gas phase optical phase modulation, the instructions comprising:
 passing a laser beam longitudinally through a tube open to air at both ends; and 
 setting air inside the tube into resonant acoustic oscillation, thereby temporally modulating the refractive index of the air, which temporally modulates the optical phase of the laser beam, 
 wherein the acoustic transducer used to excite the resonant acoustic oscillation within the tube creates acoustic oscillation such that one acoustic wavelength is slightly longer than twice the tube length. 
 
     
     
       18. The non-transient computer-readable medium of  claim 17 , further comprising:
 using an acoustic transducer to set the air inside the tube into resonant acoustic oscillation. 
 
     
     
       19. The non-transient computer-readable medium of  claim 18 , wherein the acoustic transducer is near a center of the tube. 
     
     
       20. The non-transient computer-readable medium of  claim 17 , wherein acoustic pressure oscillates at high amplitude near the center of the tube and tapers to near zero at both ends of the tube. 
     
     
       21. The non-transient computer-readable medium of  claim 17 , wherein a refractive index of the air inside the tub varies periodically with air pressure, thereby imposing a sinusoidal phase modulation with a period of acoustic resonance on the laser beam passed lengthwise through the tube.